1. Technical Field
The present invention relates generally to thermal imaging systems, and in particular to a time shared histogram chip that provides line summing, line grabbing and histogramming functions for video signal processing purposes.
2. Discussion
Scanning thermal imaging systems are used in a variety of applications, including surveillance systems and target detection/recognition systems. Such systems typically incorporate a telescopic lens assembly coupled to a scanner. The scanner scans energy from a scene through an imager lens assembly onto a detector array having a plurality of photoelectrically responsive detector elements perpendicular to the scan direction. Each of these detector elements provides an electric signal proportional to the flux of infrared light on the particular detector element. Electric signals generated from the detector elements are subsequently processed by system sensor electronics to create an image that is displayed on a system output device. To improve sensitivity, some of these systems incorporate detectors parallel to the scan direction. The output of these detectors are delayed in time from each other such that, ideally, the scanned image is output simultaneously on all of the parallel detectors. The delayed outputs are then summed (integrated). This process is referred to as time delay and integrate (TDI).
In the above-mentioned thermal imaging systems, the system sensor electronics process signals from the detector element to provide a clean output video signal to the system output device. An important component in the system electronics includes a histogram chip that collects and manipulates data taken from the video signal to allow the processor to look at the data and thereby control the video data compression functions. Associated system hardware performs line summing functions to correct channel-to-channel imbalances and to ensure detector element outputs are equal in voltage level and voltage gain. System hardware also performs video signal line grabbing functions to correct pixel misalignment associated with each of the channels output from the detector array to ensure that pixels across the output display in one row are aligned with pixels in adjacent rows.
While the prior thermal imaging systems exhibit adequate performance characteristics, there is room for advancement in the art. In particular, present design specifications require that more thermal imaging-based applications be implemented in smaller and smaller footprints. Therefore, there is a need to consolidate the separate functions of prior histogram chip and system hardware components into a smaller package. In addition, such thermal imaging systems have a relatively high associated cost of implementation due to the numerous hardware and software-based components required for implementation. Further, there is the ongoing need to increase system accuracy as much as possible.
What is needed then is a time-shared histogram chip that is capable of performing histogramming, line summing and line grabbing functions, thereby minimizing system cost and complexity and at the same time enhancing overall system accuracy.